Black Liquor Sprays Rick Wessel, Ph.D. Advisory Engineer The Babcock & Wilcox Company Outline Slide 2 Objectives and key variables Black liquor spray nozzles Droplet size distribution Spray distribution Implications for recovery boilers 1
Black Liquor Guns Slide 3 Ring header Steam-out lines LP steam line Flexible hose Shut-off valve Liquor gun Liquor gun port Liquor gun support Key Parameters for BL Spray Slide 4 Process Variables Liquor dry solids Liquor elevated boiling point Physical properties (density, viscosity, etc) Liquor burning characteristics (swelling) Operating Parameters Number and arrangement of guns Tilt or oscillation of gun barrels Nozzle type and size Firing temperature Liquor flow rate and pressure 2
Spray Characteristics Slide 5 Median droplet diameter Droplet size distribution Spray velocity Flow distribution Slide 6 Impact of Droplet Size on Trajectory Initial Droplet Diameter Small (< 1mm) Medium (1 to 2 mm) Large (> 2 mm) Smelt coalescence Swollen char Black liquor Wall deposits Char Bed Combustion air Smelt 3
Objectives for Effective Spraying Slide 7 Control droplet size (2 to 4 mm) Minimize particle carryover Deliver mostly dry liquor to bed Control height of char bed Distribute liquor spray Minimize liquor on furnace walls Create a uniform symmetrical bed shape Nozzle Types Slide 8 Swirlcone Nozzle V-Type Nozzle Splash Plate Nozzle Typical Nozzle Gun Assembly 4
Splash Plate Nozzle Geometry Slide 9 Barrel Coupling Barrel Tilt Coupling Angle Splash Plate Angle Black Liquor Looking down on a splash plate nozzle 35 plate angle 45 plate angle Swirlcone and V-Type V Nozzles Slide 10 Swirlcone V-Type Black liquor Black liquor Swirl plate Nozzle cap 5
BL Nozzle Operating Conditions Slide 11 Orifice size, in. Pressure, psi Flow, GPM Median droplet size, mm Splash Plate 0.7 1.25 15 45 25 75 2 4 Swirlcone & V-type 0.4 0.75 12 18 20 40 2-4 Black Liquor Spray Breakup Slide 12 Splash plate tip Direction of spray 6
Slide 13 Spray Size Distribution for BL Nozzles Mass Less Than D, % 100 80 60 40 20 0 Splash plate and swirlcone nozzles with hot, concentrated black liquor 0.1 1 10 Diameter/Median Diameter Median Droplet Size Slide 14 D S Dmedian = 0.290 KLKN Q T 1.23 0.62 n 0.23 0.14 Splash plate, swirlcone,, and V-type V nozzles D median = median droplet diameter K N, K L = nozzle and liquor constants S = liquor dry solids (weight fraction) T = liquor temperature, C C (non-flashing) D n = nozzle diameter, m Q = volume flow rate, m 3 /s 7
Elevated Boiling Point Slide 15 Liquor Temperature or Elevated Boiling Point ( o F) 300 290 280 270 260 250 240 230 220 Flashing Temperature Elevated Boiling Point Flashing T T BP > 9 F (5 C) Transitional 9 F 5 C Typical Range of Operation Non-Flashing 150 140 130 210 100 50 60 70 80 90 Solids Content (%) ( o C) 120 110 Three Temperature Regimes Slide 16 Non-Flashing Transitional Flashing Solids = 69%, EBP = 115 C Excess Temperature, ΔT e = T - T EBP 8
Black Liquor Flashing Slide 17 Higher nozzle velocity due to expansion of steam bubbles Non-flashing Flashing Example Nozzle Spray Conditions Slide 18 Splash plate nozzle Nozzle diameter 30/32 in (24 mm) Solids content 70 % Temperature 245 F F (118 C), transitional Volume flow rate 74.5 gpm (4.7 l/s) Liquor pressure 16.4 psig (1.13 bar) Median droplet diameter 3.3 mm Spray velocity 30 ft/s (9.1 m/s) 9
Slide 19 Effect of Nozzle Diameter on Drop Size Non-Flashing D 1.23 median Dn Note: liquor mass flow rate, temperature and solids are fixed Slide 20 Effect of Nozzle Diameter on Velocity Non-Flashing 2 V 1D n Note: liquor mass flow rate, temperature and solids are fixed 10
Slide 21 Effect of Temperature on Drop Size D median 1/T 0.14 Note: liquor mass flow rate, solids, and nozzle diameter are fixed Effect of Temperature on Velocity Slide 22 Note: liquor mass flow rate, solids, and nozzle diameter are fixed 11
Liquor Spray Distribution Slide 23 Wall Firing Small boilers 1 or 2 oscillating guns Stationary Firing Large boilers 4 to 12 fixed guns Slide 24 Predicting Spray Distribution and Deposits Based on computational analysis of the trajectories of large drops Useful for sensitivity studies Useful for initial optimization Examples for one particular boiler Demonstrates sensitivity to operating parameters Can show interactions between parameters 12
Recovery Boiler Used in Examples Slide 25 Floor dimensions Firing method Number of guns Barrel tilt Nozzle size Splash plate angle Liquor dry solids Liquor temperature 31.5 x 28.4 ft (9.6 x 8.7 m) Stationary firing 4, one at center of each wall - 20 (median) #38 (38/32 inches or 1 3 /16 ) 49 (median) 65.8% 220 F (104.4 C) non-flashing Slide 26 Impact of Barrel Tilt on Bed Shape - 10-20 - 30 13
Impact of Nozzle Size Slide 27 #34 nozzle #40 nozzle TA TA Deposition Rate (kg/hr-m 2 ) BL BL 2500 2300 2100 1900 1700 1500 1300 1100 900 700 500 300 100 SA PA SA PA Impact of Splash Plate Angle Slide 28 35 49 TA TA Deposition Rate (kg/hr-m 2 ) BL BL 2500 2300 2100 1900 1700 1500 1300 1100 900 700 500 300 100 SA PA SA PA 14
Impact of Flashing Slide 29 Non-Flashing Flashing TA TA Deposition Rate (kg/hr-m 2 ) BL BL 2500 2300 2100 1900 1700 1500 1300 1100 900 700 500 300 100 SA PA SA PA Implications for Recovery Boilers Slide 30 Select nozzle type, number, arrangement, and barrel tilt for liquor spray distribution Select nozzle size for required flow, liquor pressure and median droplet size Recognize and control flashing Flashing impacts spray velocity and droplet size Stay above or below flashing temperature If above, use temperature to control droplet size 15